The present invention is related to passenger detection systems, and in particular to passenger detection systems that can readily classify an attribute of a passenger of an automobile in which an air bag device is installed.
In general, air bag devices are used to ease the shock that a passenger experiences during an automobile collision, and as such must be stored in a stable condition in the automobile. Air bags are installed in front of the driver's and passenger's seats. Air bags may be installed in other locations.
In a typical air-bag system, the control system includes a control circuit that receives a signal from an electrical acceleration sensor (shock detection sensor), and transmits control signals to the gates of normally-open semiconductor switching elements. The switching elements are respectively connected in parallel paths between a system operating voltage and ground. Each path includes a safing sensor, a squib circuit and the switching element. The squib circuits are connected to the gas sources of the air bag devices respectively mounted on the automobile in front of the driver's seat and the front passenger seat or other locations (e.g. side airbags).
In operation, the air bag control system only deploys the driver and passenger air bags when both of the safing sensors close, and when the electrical acceleration sensor closes. In particular, the acceleration detection mechanisms of the safing sensors close their respective normally-open switches in response to an acceleration that is relatively small in comparison to the acceleration necessary to close the electrical acceleration sensor. When closed, the safing sensor applies a high voltage signal to the control circuit and to first terminals of the squib circuits. The high voltage signals from the safing sensor cause the control circuit to enter into an operational mode. Next, the control circuit confirms that the automobile is in an accident based on the signal from the electrical acceleration sensor. If the electrical acceleration sensor also detects the acceleration, the control circuit transmits control signals that close the switching elements. As a result, current flows from the system operating voltage to ground through each of the squib circuits, thereby causing respective gas sources to deploy (inflate) the driver-side air bag and the passenger-side air bag. Once deployed, the air bags protect the driver and passenger from the shock of the collision.
Passenger-side air bags are typically designed to deploy in front of the torso of an adult passenger seated in the front passenger seat. When a rear facing infant seat (hereafter RFIS) is located on the front passenger seat, it is desirable for the passenger-side air bag not to deploy. It may also be desirable for the passenger-side air bag not to deploy when a forward facing child seat (hereafter "FFCS") or child is used.
Several passenger detection sensor types have been proposed for detecting a RFCS, an FFCS or children. Such proposed sensors include (1) a weight sensor and (2) an optics sensor and image processor. The weight sensor may incorrectly detect a heavy child, or fail to detect a light-weight adult. Further, if a heavy object (such as a bag of groceries) is placed on the seat, the air bag device may be needlessly deployed in an accident. The optics sensor is expensive and the processing equipment is complex.
Since airbags deploy forcefully and quickly, sensors for determining whether any passenger is in a desirable or undesirable location are desired. Such sensors may prevent injury. By avoiding deployment of the airbag when no passenger present, replacement costs may be avoided.